Punch cards were the first __________ system used for machines.

Punch cards were the first binary system used for machines because they operated based on a simple mechanism of holes and no holes to represent information. Each punch card has a series of holes punched in specific locations to represent data, where the presence or absence of a hole corresponds to binary values—essentially, a '1' for a hole and a '0' for no hole. This foundational concept of representing information using two distinct states (on or off) is what characterizes binary systems.

While the other options may pertain to different methods of data representation, punch cards specifically do not fit the definitions of graphical, analog, or digital systems in the same way. Graphical systems involve visual representations like images or diagrams, while analog systems convey information through continuous signals. Digital systems, which utilize distinct states to represent data, can be related to punch cards, but they are a broader category that encompasses a variety of technologies developed later. Therefore, identifying punch cards as a binary system highlights their primary operational characteristics, which laid the groundwork for modern computing.